Can no longer call `typed_struct` multiple times

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

### AI Policy

- [x] I agree to follow this project's AI Policy, or I agree that AI was not used while creating this issue.

### Versions

Broke in version [v3.5.35](https://github.com/ash-project/ash/releases/tag/v3.5.35) due to this commit https://github.com/ash-project/ash/commit/0fb406aecde970ad8e6252fb82b672ab1bf6f714

### Operating system

OSX

### Current Behavior

We recently tried upgrading to v3.5.36 from v3.5.34. Once we did we got a new error

```
(ArgumentError) defstruct has already been called for EKG.Scenes.Events.ChannelFollowed, defstruct can only be called once per module
```

This module does the following:

```ex
defmodule EKG.Scenes.Events.ChannelFollowed do
use EKG.Scenes.BaseEvent

typed_struct do
field :follower_id, :string, allow_nil?: false
# ... etc ...
end
end
```

Where `EKG.Scenes.BaseEvent` is

```ex
defmodule EKG.Scenes.BaseEvent do
defmacro __using__(_opts) do
quote do
typed_struct do
field :platform, :atom, allow_nil?: false, constraints: [one_of: [:twitch, :youtube]]
# The "raw" event from original source
field :raw, :map, allow_nil?: false
end
end
end
end
```

This idea being that the base event ensured all events had those two fields.

### Reproduction

```ex
defmodule Test do
typed_struct do
field :foo, :string
end
typed_struct do
field :bar, :string
end
end

### Expected Behavior

Expect the two `typed_struct` calls to be merged as they used to be. OR a user story of how to accomplish what we were doing before

Start by reading the regression commit linked in the issue and tracing the `typed_struct` calls in `Test`, `EKG.Scenes.BaseEvent`, and `EKG.Scenes.Events.ChannelFollowed`. Reproduce the `defstruct has already been called` error, then verify either that multiple calls merge again or that the supported replacement for the base-event pattern is documented.

Written by the indexing model from the issue text.